In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beams through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions become soluble in a developing solution is called a positive-type resist material, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type resist material.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are now starting to be introduced in mass production of semiconductor elements. Furthermore, research is also being conducted into lithography techniques that use exposure light source having a wavelength shorter than these excimer lasers, such as F2 excimer lasers, electron beam, extreme ultraviolet radiation (EUV), and X ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a resolution capable of reproducing patterns of minute dimensions, and a sensitivity to these types of exposure light sources. One example of a resist material capable of satisfying these requirements is a chemically amplified resist (also referred to as a chemically amplified resist composition), which includes a base resin that displays changed alkali solubility under the action of acid, and an acid generator that generates acid upon exposure. For example, a chemically amplified positive resist contains, as a base resin, a resin which exhibits increased alkali solubility under action of acid, and an acid generator. In the formation of a resist pattern, when acid is generated from the acid generator upon exposure, the exposed portions become alkali soluble.
Until recently, polyhydroxystyrene (PHS) or derivative resins thereof in which the hydroxyl groups have been protected with acid-dissociable, dissolution-inhibiting groups (PHS-based resins), which exhibit high transparency relative to a KrF excimer laser (248 nm), have been used as the base resin of chemically amplified resists. However, because PHS-based resins contain aromatic rings such as benzene rings, their transparency is inadequate for light with wavelengths shorter than 248 nm, such as light of 193 nm. Accordingly, chemically amplified resists that use a PHS-based resin as the base resin component suffer from low levels of resolution in processes that use light of 193 nm.
As a result, resins that contain structural units derived from (meth)acrylate esters within the principal chain (acrylic resins) are now widely used as the base resins for resists (also referred to as resist compositions) that use ArF excimer laser lithography or the like, as they offer excellent transparency in the vicinity of 193 nm (see Patent Document 1).
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2003-241385